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Journal of Virology, July 2000, p. 5968-5981, Vol. 74, No. 13
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Immune Responses and Viral Replication in Long-Term
Inapparent Carrier Ponies Inoculated with Equine Infectious
Anemia Virus
Scott A.
Hammond,1,
Feng
Li,1
Brian M.
McKeon Sr.,1
Sheila J.
Cook,2
Charles J.
Issel,2 and
Ronald C.
Montelaro1,*
Department of Molecular Genetics and
Biochemistry, School of Medicine, University of Pittsburgh,
Pittsburgh, Pennsylvania 15261,1 and Gluck
Equine Research Center, Department of Veterinary Science,
University of Kentucky, Lexington, Kentucky 405462
Received 21 July 1999/Accepted 10 April 2000
Persistent infection of equids by equine infectious anemia virus
(EIAV) is typically characterized by a progression during the first
year postinfection from chronic disease with recurring disease cycles
to a long-term asymptomatic infection that is maintained indefinitely.
The goal of the current study was to perform a comprehensive longitudinal analysis of the course of virus infection and development of host immunity in experimentally infected horses as they progressed from chronic disease to long-term inapparent carriage. We previously described the evolution of EIAV genomic quasispecies (C. Leroux, C. J. Issel, and R. C. Montelaro, J. Virol.
71:9627-9639, 1997) and host immune responses (S. A. Hammond,
S. J. Cook, D. L. Lichtenstein, C. J. Issel, and R. C. Montelaro, J. Virol. 71:3840-3852, 1997) in four
experimentally infected ponies during sequential disease episodes
associated with chronic disease during the first 10 months postinfection. In the current study, we extended the studies of these
experimentally infected ponies to 3 years postinfection to characterize
the levels of virus replication and development of host immune
responses associated with the progression from chronic disease to
long-term inapparent infection. The results of these studies revealed
over a 103-fold difference in the steady-state levels of
plasma viral RNA detected during long-term inapparent infection that
correlated with the severity of chronic disease, indicating different
levels of control of virus replication during long-term inapparent
infections. Detailed analyses of antibody and cellular immune responses
in all four ponies over the 3-year course of infection revealed a similar evolution during the first year postinfection of robust humoral
and cellular immunity that then remained relatively constant during
long-term inapparent infection. These observations indicate that immune
parameters that have previously been correlated with EIAV vaccine
protection fail to provide reliable immune correlates of control of
virus replication or clinical outcome in experimental infections. Thus,
these data emphasize the differences between immunity to virus exposure
and immune control of an established viral infection and further
emphasize the need to develop and evaluate novel immunoassays to define
reliable immune correlates to vaccine and infection immunity, respectively.
*
Corresponding author. Mailing address: W1144 Biomedical
Science Tower, Department of Molecular Genetics and Biochemistry, School of Medicine, University of Pittsburgh, Pittsburgh, PA 15261. Phone: (412) 648-8869. Fax: (412) 383-8859. E-mail:
rmont{at}pop.pitt.edu.

Present address: IOMAI Corporation, Washington, DC
20037.
Journal of Virology, July 2000, p. 5968-5981, Vol. 74, No. 13
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
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